Recovery of molybdenite by flotation



United States Patent RECOVERY OF MOLYBDENITE BY FLOTATION Harry B.Henderson, 'Chuquicamata, Chile, assignor to The Anaconda Company, acorporation of Montana No Drawing. Filed Mar. 7, 1958, Ser. No. 719,708

8 Claims. ((11. 209-167) This invention relates to the separation ofmolybdenite by selective flotation from a complex ore containingmolybdenite together with various other metallic sulfides. The inventionprovides an improved process which is particularly suited for recoveringmolybdenite in high concentration from a preliminary flotationconcentrate containing large amounts of both copper sulfide and ironsulfide and only a very small amount of molybdenite.

Although molybdenite (molybdenum sulfide, M08 is found in barelydiscernible quantities practically whereever igneous rocks are known, byfar the largest molybdenite deposits found throughout the world areclosely associated with those acidic plutonic rocks which frequentlycontain relatively large concentrations of other sulfides, notablycopper sulfide and iron sulfide. Because rnolybdenite is but a minorconstituent in these complex cupriferous ores, the bulk sulfideflotation concentrates isolated from the ore contain a very smallproportion of molybdenite, usually less than 0.5 percent. In addition tothe problem of extricating and concentrating this small amount ofmolybdenite from the concentrate, ithe recovery of molybdenite isusually further complicated by a residual coating of sulfhydriccollector and frother which is carried over with the concentrate.Despite the ease with which molybdenite floats, before any molybdenitecan be selectively floated from the concentrate the residual collectorusually must be decomposed or a specific depressant employed to depressthe flotation of the bulk mineral sulfides (i.e. copper and ironsulfides).

The residual sulfhydric collector coating which adheres to the bulksulfide concentrate is generally either a thiophosphate or a xanthate,both of which may be chemically destroyed by one of two heretoforeproposed methods. In the first, the concentrate is heated to atemperature of about 100 C. either by prolonged treatment of an aqueouspulp of the concentrate with live steam or by drying the bulk sulfideconcentrate with hot flue gases. Heating of flotation concentratedestroys both types of sulfhydric collector coatings by decomposing thecollector ion. In the second method of chemically decomposing thecollector coating, the flotation concentrate is conditioned with anoxidizing agent in either an acidic or alkaline medium to oxidize thecollector coating. With either method, however, undesirable resultsaccrue, for the thermal destruction of the collector coating isexceptionally wasteful ofheat, requiring the boiling or roasting ofmassive amounts of pulp to recover a very small quantity of molybdenite,while the oxidative conditioning of the bulk sulfide flotationconcentrate with an oxidizing agent is ineflective unless the oxidationis substantially carried to'completion.

Anothermethod of inhibiting the flotation of the bulk (copper and iron)mineral sulfides while selectively flotating molybdenite is based uponthe use of certain inorganic compounds which are capable of exerting aspecific depressive effect on the flotation of copper sulfides. Theseinorganic compounds (described in the Nokes, Quigley and Pring UnitedStates Patent No. 2,492,936, granted December 27, 1949, and commonly.known as Nokes reagents) contain phosphorus, arsenic, or antimonycombined with bivalent sulfur and an inorganic cation. The effectivenessof these reagents as depressants of the bulk sulfides is more or lessimpaired, however, when the sulfide flotation concentrate iscontaminated with residual flotation agents from the preliminaryflotation operation by which it was formed (i.e. a residual collector,such as a xanthante or a thiophosphate, and a residual frother such asamyl alcohol or pine oil). To meet this problem it has been proposed toemploy the Nokes reagent depressant in conjunction with either activatedcarbon or charcoal, both of which enhance the effectiveness of thedepressant in the presence of residual flotation reagents.

These carbonaceous materials, however, have a pronounced tendency tofloat along with molybdenite, and so seriously dilute the proportion ofmolybdenum sulfide in the concentrate; moreover, the carbon must besubsequently removed from the concentrate to produce a high grade andreadily marketed molybdenum sulfide product.

I have found that a notable improvement in the recovery of molybdeniteby flotation from a bulk sulfide flotation concentrate containing arelatively very large concentration of copper is achieved when the Nokesreagent depressant is used in conjunction with a small concentration ofa dimethylpolysiloxane. By subjecting an aqueous pulp of the bulksulfide concentrate to froth flotation in the presence of the inorganic(Nokes reagent) compound and a dimethylpolysiloxane, an exceptionallygood grade of molybdenite concentrate is selectively floated, and amarkedly improved recovery of molybdenite from a material containing itin only very low concentration, is attained. Moreover, these'results aresecured without the necessity of using any activated carbon or charcoal,or heating or oxidizing the bulk mineral sulfide concentrate to destroyresidual flotation agents.

Based on these discoveries, the invention provides an improved processfor recovering molybdenite from a flotation concentrate containingcopper sulfide and molybdenite which comprises subjecting an aqueouspulp of the concentrate to froth flotation in the presence of a frothingagent, a dimethylpolysiloxane having a viscosity of at least 200centipoises at 25 C., and an inorganic compound of an element selectedfrom the group consisting of phosphorus, arsenic, and antimony, saidinorganic compound containing bivalent sulfur and an inorganic cationand being present in an amount sufiicient to depress the bulk sulfideminerals without substantial depression of molybdenum sulfide.

An extremely large number of chemically individual bulk sulfidedepressants are available for use to selectively depress the flotationof the bulk sulfides (i.e., copper sulfide and iron sulfide) withouthindering the selective flotation of molybdenite. As indicated above,these depressants are the reagents described in the aforementionedNokes, Quigley and Pring United States Patent No. 2,492,936, and areinorganic compounds which contain phosphorus, arsenic or antimonytogether with bivalent sulfur and an inorganic cation. Where thedepressant is a phosphorus compound, it may be prepared by reactingthiophosphoryl chloride (in which sulfur is already present in thebivalent state) together with either sodium hydroxide, calciumhydroxide, sodium silicate, sodium carbonate, ammonium hydroxide,ammonium phosphate, sodium phosphate or sodium borate. Another method ofpreparing phosphorus-containing depressants is based on the use ofphosphorus sulfides, notably phosphorus pentasulfide. In such cases, thephosphorus pentasulfide is reacted with either sodium hydroxide, calciumhydroxide, sodium silicate, sodium carbonate, ammonium hydroxide,ammonium carbonate, ammonium phosphate, sodium phosphate, sodium borate,calcium cyanide or sodium cyanide, all of which react with phosphoruspentasulfide to form bulk sulfide depressants.

Arsenic-containing compounds which depress the flotation of the bulkmineral sulfides but not molybdenite may be prepared by reacting arsenicsulfide with either sodium hydroxide, potassium hydroxide or calciumhydroxide, or alternatively, by reacting arsenic oxide together withsulfur and an alkali metal hydroxide. Antimony-containing depressantsmay be prepared in a similar manner, such as via the reaction ofantimony oxide, sulfur and an alkali metal hydroxide.

The dimethylpolysiloxanes, or silicone oils as they are frequentlycalled, which are used in the method of the invention, are usuallyrepresented by the formula in which n is an integer, the formularepresenting a trimethyl silyl end-blocked dimethylpolysiloxane.However, either or both the terminal and intermediary methyl groups maybe replaced or substituted in whole or in part with other organic (i.e.ethyl and phenyl) or even inorganic radicals. Even when thussubstituted, the polymers are generically known as polysiloxanes and arethe full equivalent of the dimethylpolysiloxanes. These silicone oilsare high molecular weight polymers whose viscosity varies directly withthe molecular weight. For effective use in conjunction with the Nokesreagent in carrying out the method of this invention, especially intreating concentrates containing residual flotation agents, themolecular weight of the dimethylpolysiloxane should be high enough toimpart to it a viscosity of at least 200 centipoises at 25 C.Dimethylpolysiloxanes having such high viscosities are soluble inbenzene but very sparingly soluble in water, and consequently thesesubstances are generally added to the flotation pulp in the form of anaqueous emulsion. Various thickening agents, such as silica gel, may beincorporated in the emulsion to stabilize it.

The quantities of reagents used in the process are, of course, dependentupon many factors, including the relative concentrations of molybdeniteand copper sulfide in the bulk mineral sulfide flotation concentrate andthe amount and type or organic collector and frother present. In therougher flotation of molybdenite, for example, the processing of a tonof concentrate generally requires from 2 to 5 pounds of the bulk sulfidedepressant (Nokes reagent) and from 0.1 to 0.5 pound of an oil-in-wateremulsion containing from about 5 to 30 percent of adimethylpolysiloxane. Lesser amounts of the bulk sulfide depressant arerequired in subsequent cleaner flotations; generally a further additionof from 0.25 to 0.5 pound per ton of cleaner concentrate has been foundsatisfactory in the cleaner operations.

Although further additions of the dimethylpolysiloxane may also be madeto the pulp in the subsequent cleaner flotation operations, once it hasbeen used in the rougher flotation a sufiicient quantity ordinarily iscarried over into subsequent flotation operations so that no furtheradditions are required.

'4 l The flotation reagents present in carrying out the method of theinvention need be only those present as residuals from the production ofthe original bulk sulfide concentrate. Any sulfhydric collector forsulfide min- 5 erals, and any frothing agent, may be used. Indeed, thecollector may be absent altogether, for molybdenite will float in thepresence of a frother alone. The amount of frother, and collector ifpresent, will normally be in the range from a mere trace amount toperhaps 3 pounds per ton of concentrate produced in the molybdeniterougher operations, and usually no further addition will be made in thesubsequent cleaner operations.

Any standard flotation cell may be used in both the rougher and cleanerflotations of molybdenite in accordance with the invention, includingthe standard Pagergren and subaeration types of flotation cells. Theequipment may be arranged in any convenient manner.

The applicability of using a Nokes reagent bulk sulfide depressant inconjunction with a dimethylpolysiloxane to recover molybdenite inaccordance with the process of the invention is illustrated by thefollowing two series of flotation operations which were carried out on abulk sulfide concentrate containing only about 0.04 percent molybdeniteand 10 to 13 percent copper. Table I summarizes the results achieved inthe first series of eight separate tests (designated as Tests 1 to 8),in which an aqueous pulp of the concentrate was initially heated withsteam to a temperature of about 100 C. to deactive any residualcollector and frother, and then subjected to a rougher flotation andfive cleanings, the reagents being 2 pounds of a bulk sulfide depressantper ton of concentrate in the rougher flotation, and 0.25 pound per tonin each of the subsequent cleanings. In the second series of eight tests(designated as Tests 9 to 16), which are summarized in Table H, anaqueous pulp of the concentrate was subjected to a rougher flotation andseven cleanings, using 2 pounds of a bulk sulfide depressant and 0.25pound of an aqueous (oil-in-water type) emulsion containing 30 percentby weight of a dimethylpolysiloxane (viscosity greater than 200centipoises at 25 C.) per ton of concentrate in the rougher flotation,and further addition of only 0.25 pound per ton of the sulfidedepressant in each of the subsequent seven cleanings. The Nokes reagentbulk sulfide depressant used in all of the tests was prepared byreacting 10 parts by weight of phosphorus penta' sulfide with 13 partsby weight of sodium hydroxide in aqueous solution. In the first seriesof tests (Table I) a matty, uncontrollable foam was formed during theflotation operation, but in the second series of tests (Table II) nosuch foam was formed. The test results demonstate that the depressanteifect which is exerted by the Nokes reagent on the flotation of thebulk mineral sulfides is enhanced by the concurrent use of thedimethylpolysiloxane, with the result that a high concentration ofmolybdenite and a notably low concentration of copper is recovered froma heads in which the molybdenite concentration is extremely low.

TABLE I Metallurgical results [Nokes reagent and steam treatment]Rougher Concentrate Heads, Tails, Test No. Percent Percent M0 M0 PercentPercent Percent Percent Mo Ins. Fe Cu Average--- 08 023 49. 31 2. 67 1.44 6. 77 76 TABLE II Metallurgical results [Nokes' reagent anddimethylpolyslloxane] TABLE IV Metallurgical results [Nokes reagent anddimethylpolysiloxane] ms- Rougher Concentrate 5 Heads, Tails,Concentrate Test N 0. Percent Percent Heads, Rougher Percent M M0Percent Percent Percent Percent Test N0. Percent Tails, Recov- Mo Ins.Fe Cu Mo Percent Percent Percent Per Per ery M0 M0 Ins. cent cent Mo FeCu a as a a 7 I07 I02 5337 21 1 1 11 .12 .04 47-. 40 13.80 1. 07 1. 4926.44 .05 .02 44.97 2. 90 1 86 8.20 14 .04 49.97 8. 90 76 2. 06 30. 2112 .02 52.2 3.42 0. 93 4. 19 08 .02 55. 78 3. 96 51 70 17. 85 08 0152.15 3. 34 1 13 1. 66 .13 .03 53. 43 7.16 66 77 13.64 08 02 62. 96 2.30 1. 24 2. 57 g 5 14 02 55. 31 4. 26 66 1. 47 37. 28 Ave 21 e .08 .02352.55 2.81 1.02 2.59

r g Average... .138 .026 54.34 5.10 .61 1.19 20.96

Two additional series of flotation operations covering fourteen separatetests were carried out on a bulk sulfide concentrate containing anaverage molybdenite content of only about 0.08 percent. Table IIIsummarizes the results achieved in seven of these tests (designated asTests 17 to 23), in which an aqueous pulp of the concentrate wassubjected to a rougher flotation and live cleanings, using 2 pounds ofthe Nokes reagent depressant and 2 pounds of activated carbon per ton ofconcentrate in the rougher flotation, and further additions of 0 .25pound of the sulfide depressant per ton of concentrate in each of thesubsequent cleanings. In the next seven tests (designated as Tests 24 to30), which are summarized in Table IV, an aqueous pulp of the bulkmineral concentrate was subjected to rougher flotation and fivecleanings, the reagents being 2 pounds of Nokes reagent and 0.5 pound ofan oil-in-water type emulsion containing 30 percent by weight of adimethylpolysiloxane (viscosity greater than 200 centipoises at 25 C.)per ton of concentrate in the rougher flotation with further additionsof only 0.25 pound of the sulfide depressant per ton of concentrate ineach subsequent cleaner flotation operation. As before, the Nokesreagent bulk sulfide depressant used in all of the tests was prepared byreacting parts by weight of phosphorus pentasulfide with 13 parts byweight of sodium hydroxide in aqueous solution. In the tests summarizedin Table III a matty and voluminous foam, formed; whereas the testssummarized in Table IV were untroubled by such foaming. The averageamounts of molybdenite recovered when the Nokes reagent was used inconjunction with a dimethylpolysiloxane (Table IV) was five timesgreater than when the Nokes reagent was employed with activated charcoal(Table III). In addition, the average grade of the molybdeniteconcentrate produced was greater, and its average copper contact wasless, in each of Tests 24 to 30, which employed the process of theinvention, than in Tests 17 to 23, in which activated charcoal was used.

TABLE III Metallurgical results [Nokes reagent and activated carbon]Concentrate Roughcr Percent Test N0. Heads, Tails, Recov- PcrcentPercent Percent Percent Per Per ery M0 M0 M0 Ins. cent cent M 0 Average12 034 50. 58 4. 12 93 1.45 3. 63

1 Concentrate cleaned only four times.

2 Concentrate cleaned only three tizces.

@ Average does not include test 23, since spillage occurred because 01'excessive froth.

To further illustrate the invention, a preferred embodiment is describedbelow as it was applied to the treatment of a bulk mineral sulfideflotation concentrate. The bulk mineralsulfide concentrate was isolatedfrom a complex copper ore by a conventional initial sulfidic flotationin the presence of lime, potassium ethyl xanthate (a sulfhydriccollector) and amyl alcohol (a frothing agent). This concentratecontained approximately 0.15 percent by weight of molybdenum sulfidetogether with from 25 to 30 percent by weight each of copper and ironsulfides, the remainder being silica and other insolubles.

The pulp density of this cleaner concentrate was adjusted to about 50percent solids, and the pulp con-ditioned for 1 minute in a rougherconditioner with the addition of 0.13 pound per ton of concentrate of anoilin-water type emulsion containing about 30 percent by weight of adimethylpolysiloxane having a viscosity of about 450 centipoises at 25C., and 3.5 pounds per ton of concentrate of Nokes reagent prepared byreacting 13 parts by weight of sodium hydroxide (in 20 percent aqueoussolution) together with 10 parts by weight of phosphorus pentasulfideand spray drying the resultant product.

Following the rougher conditioning, the pulp was introduced into a bankof flotation cells where it was held for a flotation time of 3 to 5minutes. The tailings from this rougher flotation, amounting to over 97percent of the heads, contained only about 0.01 percent by weight ofmolybdenite.

The rougher concentrate, having a molyhdenite concentration of about 2.5percent, was next subjected to a first cleaner flotation, and theresultant concentrate was immediately transferred to a bank of flotationcells for a second cleaner flotation. The only reagent added in thefirst and second cleaner flotations was 0.5 and 0.25 pound per ton ofconcentrate, respectively, of the Nokes reagent.

The concentrate recovered from the second cleaner flotation containedabout 20 percent by weight of molybdenite. This concentrate was regroundin a ball mill to separate the molybdenite from gauge, and the regroundconcentrate was then conditioned for approximately 5 to 6 minutes, witha further addition of 0.25 pound per ton of concentrate of the Nokesreagent. After adjusting the pulp density to 5 percent solids, it wasthen subjected to a third cleaner flotation operation. The third cleanerconcentrate contributed only about 0.2 percent of the original heads andcontained about 30 percent by weight of molybdenite.

Prior to conducting a fourth cleaner flotation, the concentrate of thethird cleaner step was conditioned for approximately 5 minutes with 0.25pound per ton of concentrate of the Nokes reagent as the sole additive,and the pulp density adjusted to 3 percent solids. The conditioned pulpwas then subjected to the fourth cleaner flotation, which yielded aconcentrate containing 51 percent by weight of molybdenite.

Next, after conditioning in the presence of about 0.5

pound per ton of sodium silicate cyanide and a further addition of 0.25pound per ton of the Nokes reagent, the concentrate recovered from thefourth cleaner flotation was subjected to the final cleaner flotation.The concentrate obtained was leached with a hot 20 percent solution ofsodium cyanide to remove residual copper. The resultant molybdeniteconcentrate contained 56 percent by weight of molybdenite, 0.6 percentby weight of iron and less than 0.3 percent by weight of copper.

I claim:

1. A process for recovering molydenite from a flotation concentratecontaining copper sulfide and molybdenite which comprises subjecting anaqueous pulp of the concentrate to froth flotation in the presence of afrothing agent, from 0.1 to 0.5 pound per ton of concentrate of anaqueous emulsion containing from to 30 percent by weight of adimethylpolysiloxane having a viscosity of at least 200 centipoises at25 C., and from 2 to 5 pounds per ton of concentrate of an inorganiccompound of an element selected from the group consisting of phosphorus,arsenic, and antimony, said inorganic compound containing bivalentsulfur and an inorganic cation.

2. A process for recovering molybdenite from a flotation concentratecontaining copper sulfide and molybdenite which comprises subjecting anaqueous pulp of the concentrate to froth flotation in the presence of afrothing agent, from 0.1 to 0.5 pound per ton of concentrate of anaqueous emulsion containing from 5 to 30 percent by weight of adimethylpolysiloxane having a viscosity of at least 200 centipoises at25 C., and from 2 to 5 pounds per ton of concentrate of an inorganiccompound of phosphorus, said inorganic compound containing bivalentsulfur and an inorganic cation.

3. A process for recovering molybdenite from a flotation concentratecontaining copper sulfide and molybdenite which comprises subjecting anaqueous pulp of the concentrate to froth flotation in the presence of afrothing agent, from 0.1 to 0.5 pound per ton of concentrate of anaqueous emulsion containing from 5 to 30 percent by weight of adimethylpolysiloxane having a viscosity of at least 200 centipoises at25 C., and the inorganic reaction product of approximately 13 parts byweight of sodium hydroxide with approximately parts by weight ofphosphorus pentasulfide in aqueous solution.

4. A process for recovering molybdenite from a flotation concentratecontaining copper sulfide and molybdenite isolated from a complexcupriferous ore and contaminated with a sulfhydric collector and afrother, which comprises subjecting an aqueous pulp of the concentrateto rougher flotation in the presence of (a) from 0.1 to 0.5 pound perton of concentrate of an aqueous emulsion containing from about 5 to 30percent by weight of a dimethylpolysiloxane having a viscosity of atleast 200 centipoises at 25 C., and (b) from 2 to 5 pounds per ton ofconcentrate of the inorganic reaction product of approximately 13 partsby weight of sodium hydroxide with approximately 10 parts by weight ofphosphorus pentasulfide in aqueous solution.

5. A process for recovering molybdenite from a flotation concentratecontaining copper sulfide and molybdenite which comprises firstsubjecting an aqueous pulp of the concentrate to a rougher flotationoperation in the presence of a frothing agent, from 0.1 to 0.5 pound perton of concentrate of an aqueous emulsion containing from 5 to 30percent by weight of a dimethylpolysiloxane having a viscosity of atleast 200 centipoises at 25 C., and from 2 to 5 pounds per ton ofconcentrate of an inorganic compound of phosphorus containing bivalentsulfur and an inorganic cation, and then subjecting an aqueous pulp ofthe rougher concentrate to at least one cleaner flotation in thepresence of a further addition of said inorganic compound.

6. A process for recovering molybdenite from a flotation concentratecontaining copper sulfide and molybdenite isolated from a complexcupriferous ore and con taminated with a sulfhydric collector and afrother, which comprises first subjecting an aqueous pulp of theconcentrate to a rougher flotation operation in the presence of (a) from0.1 to 0.5 pound per ton of concentrate of an aqueous emulsioncontainingfrom about 5 to 30 percent by weight of a dimethylpolysiloxanehaving a viscosity of at least 200 centipoises at 25 C., and (b) from 2to 5 pounds per ton of concentrate of the inorganic reaction product ofapproximately 13 parts by weight of sodium hydroxide with approximately10 parts by weight of phosphorus pentasulfide in aqueous solution, andthen subjecting an aqueous pulp of the rougher concentrate to at leastone cleaner flotation operation in the presence of a further addition offrom 0.25 to 0.5 pound per ton of concentrate of said inorganic reactionproduct.

7. A process for recovering molybdenite from a flotation concentratecontaining copper sulfide and molybdenite which comprises subjecting anaqueous pulp of the concentrate to a rougher flotation operation in thepresence of a frothing agent, from 0.1 to 0.5 pound per ton ofconcentrate of an aqueous emulsion containing from 5 to 30 percent byweight of a dirnethylpolysiloxane having a viscosity of at least 200centipoises at 25 C., and from 2 to 5 pounds per ton of concentrate ofan inorganic compound of phosphorus containing bivalent sulfur and aninorganic cation, then subjecting an aqueous pulp of the rougherconcentrate to successive cleaner flotation operations each in thepresence of said inorganic compound, and leaching the final cleanerconcentrate with a hot aqueous solution of an alkali metal cyanide todissolve substantially all of the remaining copper sulfide from themolybdenite.

8. A process for recovering molybdenite from a flotation concentratecontaining copper sufide and molybdenite isolated from a complexcupriferous ore and contaminated with a sulfhydric collector and afrother, which comprises subjecting an aqueous pulp of the concentrateto a rougher flotation operation in the presence of (a) from 0.1 to 0.5pound per ton of concentrate of an aqueous emulsion containing fromabout 5 to 30 percent by weight of dimethylpolysiloxane having aviscosity of at least 200 centipoises at 25 C., and (b) from 2 to 5pounds per ton of concentrate of the inorganic reaction product ofapproximately 13 parts by weight of sodium hydroxide with approximately10 parts by weight of phosphorus pentasulfide in aqueous solution,subjecting an aqueous pulp of the rougher concentrate to successivecleaner flotation operations each in the presence of a further additionof from 0.25 to 0.5 pound per ton of concentrate of said inorganicreaction product, and leaching the final cleaner concentrate with a hotaqueous solution of an alkali metal cyanide to dissolve substantiallyall of the remaining copper sulfide from the molybdenite.

Bickerman: Foams Theory and Industrial Applications, Reinhold, New York,1953, pages 309, 310.

Taggait: Handbook of Mineral Dressing, 1945, Section 12, pages 46 and47.

1. A PROCESS FOR RECOVERING MOLYDENITE FROM A FLOTATION CONCENTRATECONTAINING COPPER SULFIDE AND MOLYBDINITE WHICH COMPRISES SUBJECING ANAQUEOUS PULP OF THE CONCENTRATE TO FROTH FLOATION IN THE PRESENCE OF AFROTHING AGENT, FROM 0.1 TO 0.5 POUND PER TON OF CONCENTRATE OF ANAQUEOUS EMULSION CONTAINING FROM 5 TO 30 PERCENT BY WEIGHT OF ADIMETHYLPOLYSILOXANE HAVING A VISCOSITY OF AT LEAST 200 CVENTIPOISES AT25*C., AND FROM 2 TO 5 POUNDS PER TON OF CONCENTRATE OF AN INORGANICCOMPOUND OF AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF PHOSPHORUS,ARSENIC, AND ANTIMONY, SAID INORGANIC COMPOUND CONTAINING BIVALENTSULFUR AND AN INORGANIC CATION.